Device for triggering an airbag

ABSTRACT

A device for triggering an airbag having a controller, a trigger, electric lines between the controlled device and the trigger and a coil for attenuating high-frequency interference currents connected to the electric lines which in turn induces interference current into the lines as a result of an external magnetic alternating field. The attenuation of the induced interference current results from an external magnetic alternating field of the coil and a compensating coil is connected in the electric lines and arranged in the surrounding area of the coil so that the amount of current induced in the compensating coil is equal to that of the interference current induced in the coil by the external field and because they are in anti-phase, the resultant current is zero from any interference.

BACKGROUND AND SUMMARY OF THE INVENTION

This application claims the priority of German Application No. 199 42815.8, filed Sep. 8, 1999 and International Application No.PCT/EP00/08244, filed Aug. 24, 2000, the disclosures of which areexpressly incorporated by reference herein.

The invention relates to a device for actuating an airbag having acontroller, a firing device for firing the airbag and electric leadswhich connect the controller to the firing device, a coil for dampinghigh-frequency interference currents being connected into the electricleads, which coil can in turn induce interference currents in the leadsto the firing means if an external electromagnetic interference field ispresent.

For actuating airbags in motor vehicles, circuits are known which have acontroller via which a firing device for firing the airbag is actuated.A firing device and be firing caps which fire, for example, a gascartridge if the actuation current at the input of the firing capexceeds a threshold value.

In order to attenuate the interference currents which were induced inthe electric leads by strong electromagnetic fields, a coil is alreadyconnected into the electric leads between the controller and the firingcap. The coil reduces, in particular, high-frequency interferencecurrents in the leads. The coil is electrically connected to the firingcap in such a way that the length of the electric leads is at a minimum.In the case of an external magnetic field, not generated by the coilitself, the coil induces interference currents in the electric leads.The behaviour is comparable to the secondary winding of a transformer ifthe magnetic flow flowing through the core is considered as the externalelectromagnetic field.

German Patent DE 299 00 178 U1 discloses a seat-belt pretensioningdevice with a gas generator, in which a circuit with a coil is providedwithin a cylindrical housing, as a result of which relatively highfrequency interference signals cannot get to the ignition system.

German Patent DE 4 136 248 A1 discloses a coil plug which has two coilswound in opposite directions around the same core within a plug housing.The coils are arranged in electric leads which are independent of oneanother, neither the wiring nor the function of the two coils beingexplained in more detail.

The object of the present invention is to configure and develop a deviceof the type mentioned above in such a way that the external effects of amagnetic field on the coil are compensated and, as a result, theinterference currents in the leads are reduced.

Accordingly, in order to compensate the interference current caused bythe external magnetic field in the coil, a compensation coil isconnected into the electric leads and arranged in the vicinity of thecoil in such a way that the induced compensation currents caused as aresult of the external magnetic field in the compensation coil areopposed to the interference currents. As a result, the currents causedby the external magnetic field cancel one another out and in addition,as in the prior art also, the high-frequency currents within theelectric leads are filtered out.

According to the invention it has been recognized that the influence ofan external magnetic field in the coil can be advantageously compensatedby a compensation coil. Here, in addition, by virtue of suitabledimensioning, the high-frequency currents in the electric leads arereduced by the alternating current resistance of the coils connected inseries, as was already the case when there was only one coil. At thesame time, the coils which are arranged antiparallel considerably reducethe overall interference currents in the coil which are induced as aresult of an external magnetic field. The compensation coil thus reducesthe negative effects which are produced owing to the externalinterference field.

The coil and the compensation coil are preferably provided in the samelead and connected in series there. As a result, the externalelectromagnetic field in the two coils generates the currents which arethe same, but act in opposite directions. By means of the dimensioning,embodiment and arrangement of the coils, it is then possible for thecurrents, which are induced by the external interference field, to bedirected in opposite directions and have the same strengths so that theycancel one another out. Therefore, an external interference field doesnot result in any additional interference currents at the load to beprotected, in particular a firing cap. As a result of the arrangement ofthe coils, the high-frequency interference currents in the leads and thecurrents induced by an external magnetic field in the coil areminimized.

The compensation coil is preferably arranged antiparallel with respectto the coil. Because the two coils are connected in series, the windingsof the two coils then run with respect to one another in such a way thatcoil fields in opposite directions are produced. For this purpose, onthe one hand, the height of the winding and on the other hand the senseof the winding in the winding direction can be adapted.

In order to change the induced current and thus determine thecompensation behaviour of the compensation coil, the material of thecoil core or the orientation of the coil winding or the number ofwindings can be adapted. Because the same current flows through thewindings of the two coils because the series connection of the coils,the coil field is preferably adapted by means of the parametersmentioned above. For this reason, the induced total current ofdifferently wound coils can still compensate one another (become zero)if, for example, different materials are used for the two coils andtheir electromagnetic fields are tuned for compensation.

In another development of the invention, the coil core is embodied as aclosed core around which either the coil or the compensation coil orboth coils are wound. When only a single annular core is used, the coiland the compensation coil can be combined to form a composite coil sothat only the composite coil is wound around the annular core. The coilcore is in particular embodied as an annular core. The annular core canhave here a circular cross section or a cross section which isessentially rectangular, the annular core being cylindrical. The annularcore then has the shape of a torus which is approximated to a lateralsurface of a cylinder. In this case, a coil winding is not essentiallycircular but rather of rectangular or oval construction in accordancewith the cross section.

With respect to an embodiment with two annular cores it has been foundthat when there is one coil wound on the first annular core and onecompensation coil wound on the second annular core, the two coils areeach provided only on one half of an annulus. If, given annular coreswhich are arranged in parallel one next to the other, they areconsidered in the direction of their common axis, the coil on the frontannular core is, for example, wound in the viewing direction only aroundthe right-hand side of the annulus and the compensation core on the rearannular coil is wound only around the left-hand side of the annulus.

The winding heights, i.e. the pitches of the windings, are arranged atan equal distance from one another. As a result, the induced totalcurrent as a result of an external magnetic field is effectivelyeliminated. For an optimum function, the pitches of the windings must bearranged at the same distance from one another, specifically over theentire casing of the core. Any deviation from this uniform windingdegrades the desired compensation result.

In a particularly preferred development of the invention, a plug isprovided in the leads between the controller and the firing means and acoil is arranged within the plug or in the region of the plug. The coilcan be arranged within an insulating material, specifically even on theoutside of the plug, but an arrangement of the coil within the housingof the plug is of particular advantage. In this case it is particularlyadvantageous to encapsulate the coil. For this purpose, the housing canbe adapted to the outer shape of the coil. Depending on the outer shapeof the coil, the housing is then essentially cylindrical or cuboidand/or for example also water-repellent.

According to the invention, the coil and the compensation coil can bearranged within the housing of the plug. It is then best to constructthe housing of the plug in two parts and can be opened out when it isequipped with plug parts. Both coils can be arranged within the housingwith axes which are parallel with one another. For this purpose, twoclosed or interrupted annular cores can be arranged adjacent to oneanother. The coil can be wound around an annular core and thecompensation coil can be wound around the other annular core, and bothcoils can be insulated from one another within the housing. Because bothcoils are connected in series, a lead is first wound around a coil corein order to form a coil and then around the other coil core in order toform the other coil, or the compensation coil. Both coils can be woundon half a side in the viewing direction parallel to the common axis ofthe annular cores, and offset laterally with respect to one another. Asa result, the capacitive coupling of the two coils is reduced. This isadvantageous if the interference currents are coupled in the region ofthe feeder line to the coils and a sufficiently good damping of theinterference is to be achieved.

As indicated previously, it is, however, also possible to provide justone annular core onto which a composite coil is wound, said compositecoil forming the coil in one part and the compensation coil in the otherpart. The effects generated by an external field in the part of thecomposite coil which forms the compensation coil eliminate the effectsformed by the same external electromagnetic field in the other part ofthe composite coil. The other part of the composite coil forms here thecoil which was originally provided for filtering the high-frequencycurrents.

BRIEF DESCRIPTION OF THE DRAWING

There are various possible ways of advantageously configuring anddeveloping the teaching of the present invention. For this purpose, onthe one hand, reference should be made to the subordinate claims and, onthe other hand, to the following explanation of a plurality ofembodiments. In the drawings, in each case in a schematicrepresentation,

FIG. 1 shows a view of the coil which is provided in the electric leadand has an electromagnetic field and compensation coil which is arrangedantiparallel with respect thereto and has an opposing field according tothe present invention,

FIG. 2 shows a view of an annular core with a coil which is woundthereon and a compensation coil according to a first embodiment of thepresent invention, and

FIG. 3 shows a plan view of an opened housing of a plug part with plugcontacts, a coil and a compensation coil according to a third embodimentof the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The device 1 for actuating an airbag 2 has a controller 3 which isconnected via electric leads 4 to a firing cap 5. The firing cap 5 firesthe airbag 2 if the current flowing through it exceeds a limiting value.A coil 6 which is intended to dampen the interference currents on theelectric leads 4 is provided in the electric leads 4 between thecontroller 3 and the firing cap 5.

The interference currents are generated mainly by coupling ofelectromagnetic fields into the electric leads 4. These are usuallyhigh-frequency interference currents. The internal resistance of thecoil 6 rises linearly with the frequency of the interference currents sothat the flow of current through the coil 6 is restricted at highfrequencies. Here, the coil 6 itself induces interference currents inthe electric leads 4 if an external interference field is present.

A compensation coil 8 is arranged adjacent to the coil 6 and is orientedwith respect to it in such a way that, in the presence of an externalmagnetic field, a current which is directed in the opposite direction tothe megnetic field current, and with the same magnitude, is induced sothat the induced total current becomes zero. Here, the compensation coil8 is connected to the coil 6 in such a way that its damping effect withrespect to high-frequency interference sources in the leads 4 is notcancelled out but rather increased. The compensation coil 8 is providedin the same way as the coil 6 in terms of number of turns, material andembodiment. The compensation coil 8 is dimensioned so that the dampingeffect on the high-frequency interference currents is not cancelled. Inaddition, the coil 6 and the compensation coil 8 are connected andarranged in such a way that in the case of an externally appliedmagnetic field, no current is induced in the electric leads 4 to thefiring cap. The two coils 6 and 8 are connected to one another in such away that the sum of the induced voltages of the coils which areconnected in series becomes zero. As a result, further interferencecurrents are not generated in the electric leads 4.

In the embodiment illustrated in FIG. 1, both coils 6 and 8 are orientedprecisely antiparallel with respect to one another, and therefore havewindings in the same direction but with a reversed connection sequence,and are electrically connected to one another. This arrangement is alsoreferred to according to the invention as antiparallel series connectionof the coil 6 and of the compensation coil 8. The requirement forparallel orientation with extremely small spacing is necessary becausein the case of a non-homogenous field the differences in the currentflowing through the two coils 6 and 8 is as small as possible.

In FIG. 2, the coil 6 and the compensation coil 8 are wound on a commonclosed coil core 10. The coil 6 is wound around a limb 11 and thecompensation coil 8 is wound around a limb 11, lying opposite, of theclosed coil core 12. Both coils 6 and 8 are correspondingly wound in thesame direction with antiphase actuation. The external interference fieldis designated by 24.

According to the described arrangement it is possible to achieve asignificant reduction in the coupling of external electromagneticalternating fields 24, in practice, by a reduction by at least a factorof 8. In order to prevent the resonance frequency of the two coils 6,8being displaced towards relatively low frequencies in comparison to onecoil, the inductance of the two coils 6,8 in the double-inductorembodiment can be half the value of the inductance of thesingle-inductor embodiment.

Finally, FIG. 3 also shows an embodiment for a motor vehicle such as isused in conjunction with an airbag. The coil 6 and the compensation coil8 are provided within a housing 14 of a plug-type connector 15 which isarranged between the controller 3 and the firing cap 5. In addition, ineach case, a plug contact 16,17 and the corresponding sockets 18 and 19of two separate leads 20,21 are arranged within the housing 14. The twocoils are connected into an electric lead 21, in series. The coil 6 andthe compensation coil 8 are wound onto separate coil cores 22 and 23which are arranged in parallel with one another. The coil axes in thisembodiment are arranged in parallel with one another and the winding isprovided again in the same direction around both cores, but is actuatedin antiphase. The housing of the plug-type connector in this embodimentis very compact and is designed so as to be capable of being opened outin order to facilitate the equipping process.

What is claimed is:
 1. A device for actuating an airbag comprising: acontroller, a firing means for firing the airbag, electric leads whichconnect the controller to the firing means, a damping coil connectedinto the electric leads for damping high-frequency interferencecurrents, said coil inducing interference currents in the leads to thefiring means in the presence of an external electromagnetic interferencefield, a compensation coil connected into the electric leads in order toreduce the influence of the external electromagnetic interference fieldand wherein said compensation coil is arranged in the vicinity of thedamping coil in such a way that the induced current of the compensationcoil counteracts the interference current induced by the externalinterference field in the damping coil, and wherein one end of thedamping coil is electrically connected to one end of the compensationcoil wherein the damping coil and the compensation coil are connected inseries in the same electric lead.
 2. The device according to claim 1,wherein, as a result of the arrangement of the compensation coil withrespect to the damping coil, the suppression of the coupledelectromagnetic interference fields is not adversely influenced incomparison with an arrangement with only said damping coil without saidcompensation coil.
 3. The device according to claim 1, wherein thecompensation coil is arranged in the same winding direction and withantiphase actuation, with respect to the damping coil.
 4. The deviceaccording to one of claim 1, wherein the damping coil and thecompensation coil have a coil core which is at least one of made of thesame material, and has the same coil winding orientation and has thesame number of coil windings.
 5. The device according to one of claim 1,wherein a coil core is provided around which the damping coil and thecompensation coil are wound.
 6. A device for actuating an airbagcomprising: a controller, a firing means for firing the airbag, electricleads which connect the controller to the firing means, a damping coilconnected into the electric leads for damping high-frequencyinterference currents, said coil inducing interference currents in theleads to the firing means in the presence of an external electromagneticinterference field, a compensation coil connected into the electricleads in order to reduce the influence of the external electromagneticinterference field and wherein said compensation coil is arranged in thevicinity of the damping coil in such a way that the induced current ofthe compensation coil counteracts the interference current induced bythe external interference field in the damping coil, and wherein one endof the damping coil is electrically connected to one end of thecompensation coil, wherein the coil core is embodied as a closed core.7. The device according to claim 6, wherein the closed coil core isembodied as a cylindrical ring.
 8. The device according to claim 6,wherein the pitches of the coil windings are one of equal magnitude andare distributed uniformly over the entire core casing.
 9. The deviceaccording to claim 6, wherein a plug-type connector is provided in theleads between the controller and the firing means, and at least one ofthe coils is arranged in the region of, the plug-type connector.
 10. Thedevice according to claim 9, wherein the housing of the plug-typeconnector is essentially cylindrical or cuboid.
 11. The device accordingto one of claim 9, wherein the plug is at least of multi-partconstruction and the damping coil and the compensation coil are arrangedwithin a plug part of the plug-type connector.
 12. The device accordingto claim 9, wherein the two coils are arranged within the plug part withthe two coil axes arranged parallel to one another.
 13. The deviceaccording to claim 6, wherein at least one of the coils is arrangedwithin the housing of the firing means.
 14. The device according toclaim 6, wherein the coils are arranged so that they fit snugly within ahousing.
 15. The device according to claim 6, wherein the electric leadfrom a contact of a plug-type connector is first wound around a coilcore in order to form the core and then around a second coil corearranged parallel thereto in order to form the compensation coil.